In the systemic treatment of anaerobic infections a parenteral mode of administration is advantageous for patients who are seriously ill and for whom oral administration is not feasible or may be considered to be insufficiently incisive. Heretofore, a practical way of administering a parenteral dose of metronidazole was not available since the aqueous solubility of metronidazole is only about 100 mg./10 ml. and a practical dosage is in the 500-650 mg./10 ml. range. Those skilled in the art recognize the practical advantages of a single 10 ml. injectable dosage form as opposed to the large volume of solution which would be needed to administer a 500-650 mg. dose of metronidazole in an aqueous solution. Thus, this invention provides a convenient and practical dosage form for the systemic treatment of anaerobic infections.
Generally, parenteral solutions are preferable for injections since they avoid the disadvantages inherent in suspensions, such as nonuniform dosage, caking, and possible slow release of the medicament when it is not desired. However, when wholly aqueous solvent systems are unsuitable, the choice of a nonaqueous system requires consideration of numerous parameters. The chosen solvent system must be nontoxic, nonirritating, and nonsensitizing. It also must exert no pharmacologic activity of its own, nor adversely affect the action of the drug. Additionally, the system must be stable under normal conditions of pharmaceutical use and not adversely affect the stability of the drug. The viscosity must be such as to allow for ease of injection, and the solvent must remain fluid over a fairly wide temperature range. Other considerations are water and body fluid miscibility, the degree of flammability, availability, source of supply and constant purity.